Ullman (Compiler Design) Edition 2 Exercise 3.3 Question 2 (Page No. 125)

Question

 Describe the languages denoted by the following regular expressions:

1. $a(a\mid b)^{\ast}a.$
2. $((\epsilon\mid a)b^{\ast})^{\ast}.$
3. $(a\mid b)^{\ast}a(a\mid b)(a\mid b).$
4. $a^{\ast}ba^{\ast}ba^{\ast}ba^{\ast}.$
5. $(aa\mid bb)^{\ast}((ab\mid ba)(aa\mid bb)^{\ast}(ab\mid ba)(aa\mid bb)^{\ast})^{\ast}.$

Answer 1

a). start and end with a.

b). (a+b)* or we can say universal set on symbols (a,b).

c). end with aaa or aab or aba or abb.

d). containing exactly 3 b's.

e). m solving (i will post (e) asap.)

correct me if wrong..

Comments

can we describe c) as third last symbola a

---

@Arnabh Gangwar

e). even no of a’s and b’s.